The invention relates generally to engines, and more specifically to engines using more than one fuel.
Compression-ignition engines, such as diesel engines, operate by directly injecting a fuel (e.g., diesel fuel) into compressed air in one or more piston-cylinder assemblies, such that the heat of the compressed air ignites the fuel-air mixture. Compression-ignition engines also can include a glow plug or grid heater to provide heat to ensure ignition, particularly during cold start conditions. The direct fuel injection atomizes the fuel into droplets, which evaporate and mix with the compressed air in the combustion chambers of the piston-cylinder assemblies. Typically, compression-ignition engines operate at a relatively higher compression ratio than spark ignition engines. The compression ratio directly affects the engine performance, efficiency, exhaust pollutants, and other engine characteristics. In addition, the fuel-air ratio affects engine performance, efficiency, exhaust pollutants, and other engine characteristics. Exhaust emissions generally include pollutants such as carbon oxides (e.g., carbon monoxide), nitrogen oxides (NOx), sulfur oxides (SOx), and particulate matter (PM). The amount and relative proportion of these pollutants varies according to the fuel-air mixture, compression ratio, injection timing, environmental conditions (e.g., atmospheric pressure, temperature, etc.), and so forth.
A dual-fuel engine is an alternative internal combustion engine designed to run on more than one fuel, for example, natural gas and diesel, each stored in separate vessels. Such engines are capable of burning varying proportions of the resulting blend of fuels in the combustion chamber and the fuel injection or spark timing may be adjusted according to the blend of fuels in the combustion chamber. For dual fuel operation where one of the fuel is premixed with air, a reduction in nitrogen oxide (NOx) and particulate matter (PM) emissions is enabled by combusting a relatively larger fraction of the premixed fuel. However, one challenge is that some of the air-fuel mixture is trapped at the crevices proximate to an edge of the piston, resulting in efficiency loss and increased hydrocarbon and carbon monoxide emissions. In certain cases, the exhaust emissions may be subjected to after treatment, but the energy associated with the exhaust emissions is not used to generate useful work.
There is a need for an improved system and method for engines operating on more than one fuel.